LTC1879 1.2A Synchronous Step-Down Regulator with 15µA Quiescent Current UFEATURESDESCRIPTIO ■ High Efficiency: Up to 95% The LTC®1879 is a high efficiency monolithic synchro- ■ Low Quiescent Current: Only 15 µ A with No Load nous buck regulator using a constant frequency, current ■ 550kHz Constant Frequency Operation mode architecture. Operating supply current is only 15µA ■ 2.65V to 10V Input Voltage Range with no load and drops to < 1µA in shutdown. The input ■ VOUT from 0.8V to VIN, IOUT to 1.2A supply voltage range of 2.65V to 10V makes the LTC1879 ■ True PLL Frequency Locking from 350kHz to 750kHz ideally suited for both single and dual Li-Ion battery-pow- ■ Power Good Output Voltage Monitor ered applications. 100% duty cycle provides low dropout ■ Low Dropout Operation: 100% Duty Cycle operation, extending battery life in portable systems. ■ Burst Mode® or Pulse Skipping Operation The switching frequency is internally set to 550kHz, allow- ■ Current Mode Operation for Excellent Line and Load ing the use of small surface mount inductors and capaci- Transient Response tors. For noise sensitive applications, the LTC1879 can be ■ Shutdown Mode Draws < 1µA Supply Current externally synchronized from 350kHz to 750kHz. Burst ■ ±2% Output Voltage Accuracy Mode operation is inhibited during synchronization or ■ Overcurrent and Overtemperature Protected when the SYNC/MODE pin is pulled low. ■ Available in 16-Lead SSOP Package The internal synchronous rectifier switch increases effi- U ciency and eliminates the need for an external Schottky APPLICATIO S diode. Low output voltages are easily supported with a ■ Cellular Telephones 0.8V feedback reference voltage. The LTC1879 is available in a 16-lead SSOP package. ■ Portable Computers ■ Wireless Modems , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. UTYPICAL APPLICATIOHigh Efficiency Step-Down ConverterEfficiency vs Output Load Current VIN 100 2.65V TO 10V 13 C V IN IN = 3.6V 10µF SV 90 IN 2 8, 9 RUN/SS PVIN 80 VIN = 7.2V 15 5, 12 L1 SYNC/MODE SWP 6.2µH 70 V LTC1879 OUT* VIN = 10V 14 6, 11 3.1V PGOOD SWN 60 EFFICIENCY (%) 150k C 4 7, 10 OUT I 47µF 50 TH PGND Burst Mode OPERATION 47pF 220pF 3 40 VFB VOUT = 3.1V SGND 80.6k L = 6.2µH 28.0k 30 1 0.1 1 10 100 1000 1879 TA01a OUPUT CURRENT (mA) CIN: TAIYO YUDEN CERAMIC LMK325BJ106MN 1879 TA01b COUT: TDK CERAMIC C4532X5ROJ476M L1: TOKO A921CY6R2M *VOUT CONNECTED TO VIN (MINUS SWITCH AND L1 VOLTAGE DROP) FOR 2.65V < VIN < 3.1V 1879f 1
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